Major strides have been made in the development of methods for synthesizing and controlling the shapes of metallic nanocrystals. Such particles have been used in optics (Barnes, et al., Nature 424: 824-830 (2003); Eustis, et al. Chem. Soc. Rev. 217: 209-217 (2006)) catalysts (Narayanan, et al. J. Phys. Chem. B 109: 12663-12676 (2005)), and biological diagnostics (Mulvaney, et al. Langmuir 19: 4784-4790 (2003); Cerruti, et al. Anal. Chem. 78: 3282-3288 (2006); Elghanian, et al. Science 277: 1078-1081 (1997)). Nanocrystal size and shape are extremely important parameters because they substantially affect the physical and chemical properties of the nanocrystals. Toward this end, a variety of new non-spherical nanostructures have been made including rods (Orendorff, et al. Small 2: 636-639 (2002); Murphy, et al. J. Phys. Chem B 109: 13857-13870 (2005); Kim, et al. J. Am. Chem. Soc. 124: 14316-14317 (2002)), boxes (Xiong, et al. Angew. Chem. Int. Ed. 44:7913-7917 (2005)), shells (Radloff, et al. Nano Lett. 4:1323-1327 (2004)), tetrahedra (Almadi, et al. Science 272:1924-1926 (1996)), cubes (Sun, et al. Science 298:2176-2179 (2002); Kim, et al. Angew. Chem. Int. Ed. 43: 3673-3677 (2004)), and prisms (Jin, et al. Science 294:1901-1903 (2001); Jin, et al. Nature 425:487-490 (2003); Metraux, et al. Adv. Mater. 17:12-415 (2005); Millstone, et al. Adv. Funct. Mater. 6:1209-1214 (2006)). Each of these structures exhibit unique plasmonic properties that depend upon their size and shape.
Silver is particularly interesting because silver triangular nanoprisms can be prepared by either a thermal or a photochemical method. The current photoreaction used to generate silver nanoprisms provides prismatic nanocrystals by irradiating a mixture of spherical nanoparticles, which have a relatively polydisperse size distribution, at two wavelengths: one that suppresses prism fusion and one that facilitates slow growth of the prism until the prism no longer absorbs this wavelength light. If only single wavelength of light is used these two processes, prism fusion and prism growth, generate a bimodal distribution of silver nanoprisms. The larger prisms have an edge length that is about twice the edge length of the smaller prisms. While the prism fusion process is interesting, it synthetically limits the preparation of monodisperse samples of one prism size. Thus, a need exists for processes which allow for monodisperse prism formation of both small (Type I) silver nanoprisms and large (Type II) silver nanoprisms.